Hydraulic brake



Nov. 16, 194s. N. o. MYRLESTAD 2,453,808

HYDRAULIC BRAKE Filed Feb. 12, -1947 y 2 sheets-sneer 1 FIG. I.

N. MYKLESTAD Nov. 16, 1948 HYDRAULIC BRAKE 2 .Shoetfs-Shheet 2 Filed Feb. 12, 1947 o o OO Patented Nov. 16, 194s UNITED STATES PATENT OFFICE HYDRAULIC BRAKE i Nils O. Myklestad, Pasadena, Calif.

Application February 12, i947, serial No. '727,960

(ci. 18s-152) 7 Claims. l

This invention relates to improvements in actuating type.

In the ordinary brake of this type there are usually two brake shoes which are pushed against the inside of the rotating brake drum by means of hydraulic pressure applied to one end of each shoe through the medium of two pistons sliding in a common cylinder, the other end of each shoe is hinged to a flxiel frame so that the shoe is free to rotate. In a`self-actuating brake the hinge axis for each shoe is located a considerable distance inside the drum sol that the friction force on one shoe will greatly aid in turning the shoe about its hinge, and thereby push it against the drum for rotation of the drum in one direction, while the friction force on the other shoe will have the same effect on it for rotation in the other direction. This makes the brake selfactuating as one shoe is always actuated by the friction force itself. An objection to such a construction, however, resides in the fact that it is very sensitive to variationslin the coefficient of friction between the brake lining, which is at tached to the outside of each shoe, and the inside of the drum. A small increase in the value of this coefficient will make the brake much more self-actuating, which is dangerous, while a small decrease in the friction coefficient. means that a greatly increased pressure will be required in order to obtain the same braking torque.

The object of the present invention is to provide an improved brake in which the hinges of the brake shoes are movably mounted and have their movements in turn controlled by hydraulic pressure in such a way that the center of pressure between the drum and the self-actuated brake -shoe will be shifted in accordance with any due to an increase, or decrease, in the coefficient of friction. It will also prevent the brake from becoming self-locking at any possible value of the coefli'cient of friction.

With the foregoing and other objects in view, which will be made manifest in the following gaged and partially engaged positions respectively.

Referring to the accompanying drawing, wherein similar reference characters designate similar parts throughout, the brake comprises a drum I which is attached to shaft 22 and rotates with the wheel, which it carries. The stationary hub 20 is bolted to flange 2I and carries brackets II and I8. Bracket I8 holds cylinder 8 in which pistons 9 and Il) are free to move under the action of spring I9 and hydraulic pressure in cylinder 8. Suitable seals are employed to prevent the brake fluid from leaking past pistons 9 and I0, said'iiuid being fed to cylinder 8 through tube 23. Brake shoes 2 an 3 carrying linings 4 and 5, respectively, are pivotable about cylindrical rods 25 and 26 attached to their upper ends, the rods fitting in corresponding grooves in blocks I2 and I3, respectively. The lower ends of the shoes are secured to ball pivots 21 and 28 which contact the pistons S-andf'lii, respectively,

' contact being maintained at all times-by means is applied to the pistons 9 and I0. While the detailed description and specifically pointed out in the appended claims, reference is made to the accompanying drawing for an illustrative embodiment of the invention, wherein:

' Figure 1' is a diametrically vertical section ball pivots are constantly bearing against the pistons 9 and I0, they are not secured thereto and hence are free to move vertically relative to the pistons. Blocks I2 and I3 are slidably mounted in corresponding grooves in bracket Il, their downward motion being checked by shoulders Ila and IIb in said bracket while their upward motion is controlled .by lever I6 'the two knife edges lliavand IGbv of which rest in corresponding grooves in-'piston I5, said piston being free to move in cylinder il its motion being controlled by disk spring I1 and hydraulic pressure produced by brake fluid entering through tube 23. Cylinder I4 is rigidly attached to bracket II,4 and suitable seals are used to prevent leakage of brake fluid between piston l5 and said cylinder. l

Generally, the operation of my device is as follows: if the drum I is rotating and if the coefficient of friction of the lining is normal, actuatin of the brake pedal to engage the'brake causes the block I 2 to assume an intermediate position such as shown in Fig. 1. If the friction is greater than normal. the effect is to shift the entire shoe 2 upwards to relieve the pressure exerted byithe toe portion of the shoe and thereby to decrease the self-actuating tendency of thc brake. If the friction is less than normal there is a corresponding reduction in the self-actuating tendency with a consequent decrease in the upward force exerted by the shoe. In this event. fluid pressure in cylinder I4 is suilicient to overcome the upward force to move block I2 downwards to increase the pressure of the toe portion against the drum and thereby to increase the selfactuating tendencywithout a corresponding increase in force actually exerted at the brake pedal.

The operation of the brake as just described is performed by the specific parts of the device substantially as follows: When the brake is disengaged shoes 2 and 3 are held away from drum I by means of springs 6 and 1, and blocks I2 and I3 are held down against the shoulders IIa and IIb of bracket II by means of disk spring I'I. When the brake is being engaged fluid is fed from the master cylinder. which is actuated by the brake pedal, through tube 23 to cylinders 8 and Il, and hydraulic pressure on pistons 9 and I0 causes .the shoes 2 and 3 to pivot around the rods 25 and 26 to push the toe portions 29 and 30 of each shoe against drum I. It will now be assumed that the drum is rotating in a counterclockwise direction so that shoe 2 will do most of the braking and the various parts are in the position shown in Fig. 4. The friction between drum I and lining 4 will now aid in turning shoe 2`about its pivot axis thereby pressing the entire shoe against the drum and increasing the pressure between said drum and -lining 4 which again will increase the braking action by turn'- ing the shoe further. This makes the brake selfactuating. It is obvious that the degree to which the brake is self-actuating is dependent on the cceflicient of friction between drum I and lining 4 as long as block I2 does not move; this is the case in an ordinary self-actuating brake. In the brake under discussion, however, the vertical reaction on block I2 will always be in a denite ratio to the actuating force on piston 9 due to the factthat cylinders 8 and I4 are connected through tube 23; this ratio of forces is so determined as to give approximately uniform prestoe portion 30 more firmly against the drum and thereby to increase the self-actuation of the brake. It will of course be appreciated that the total required motion of block I2, and hence of piston I5, is exceedingly small so that no large transfers of brake fluid will take place during such motion.

As long as drum I is rotating in a counterclockwise direction block I3 will always rest against the corresponding shoulder or stop IIa in bracket II while block I2 will center itself in accordance with the value of the coemcient of friction. On the other hand, when drum I is rotating in a clockwise direction the roles of blocks I2 and I3 will be reversed as will the roles of other corresponding left and right hand parts.

Theoretical calculations for a brake of the design shown in Figuresy 1 and 2 show that for this brake the ratio of braking torque to actuating force is much less dependent on the coeillcient oi friction than is the case for an ordinary selfactuating brake, assuming that this ratio is the ysame for both brakes at the design value of the Icoefficient of friction.

Various changes may be made in the details of construction of the safety brake without departing from the spirit and scope of the invention as defined by the appended claims.

Iclalm:

1. In a brake for a rotating cylindrical drum; an arcuate shoe adapted to be moved into engagement with the inner surface of said drum:

a separate mounting member for each end of the shoe, said mounting members providing for at least limited movement of said shoe in a direction generally parallel to a chord through the ends thereof; an actuating arrangement for moving the member at one end of the shoe in a direction generally normal to said chord to cause engagement of that end of the shoe with the drum with a desired actuating force; and means operative on the other mounting member for urging it generally radially inwardly with a force having a predetermined ratio to said actuating Y force.

sure on lining 4 for the design value of the copiston I5. Suppose now the coefficient of friction I increases above the design value due to sand or grit contaminating the linings, or for any reason; then the friction force on shoe 2, which acts predominantly upward, will also increase and move block I2 a small distance upward until the pressure on lining 4 has been redistributed to the point where equilibrium of forces has again been established. The pressure has now been increased on the upper part of lining 4 to press the heel portion 3i more tightly against the drum and decreased on the lower or toe part 30 which counteracts the increase in self-actuation due to the increase in the value of the coemcient of friction. The opposite is true when the coeiiicient of friction decreases for example, when the lining becomes wet. lThe device is so constructed that there is always some clearance between the lower end of block I2 and the corresponding shoulder or stop I I b in bracket I I when the brake is engaged, so that block I2 also is free t`o move downward when thecoefiicient of 2. In a brake for a rotating cylindrical drum:

gagement with the inner surface of said drum; a separate mounting member for each end of the shoe, said mounting members providing for at least limited movement of said shoe in a direction generally parallel to a chord through the ends thereof; a hydraulic actuating arrangement for moving the member at one end of the shoe in a direction generally normal to said chord to cause engagement of that end of the shoe with the drum with a desired actuating force; and a hydraulic arrangement operative on the other mounting member, said two hydraulic arrangements being in open communication during actuation of the brake for urging said other mounting member generally radially inwardly with a force having a predeterminedratio to said actuating force.

3. Apparatus of the character claimed in claim 2, wherein said mounting members each also provide for at least limited pivotal movement of the end of the shoe carried thereby.

4. Apparatus of the character claimed in claim 2, wherein said mounting members each also provide for at least limited pivotal movement of the end of the shoe carried thereby, and wherein a fixed stop limits the inward movement of said 5. other mounting member and a spring holds this last mentioned member against the stop in the absence of brake actuating force.

5. In a self-energizing brake for a rotatimr cylindrical drum having a pair of arcuate shoes therein and a hydraulicactuating arrangement for moving one end of each shoe' into engagement with the drum with a desired actuating force, an equalizing arrangement including: separate mounting members for the other ends of each of said shoes, each member providing for at least limited pivotal movement of that end of each shoe and for at least limited movement of each shoe in a direction generally parallel to a.

chord through the ends thereof; xed stops limit? ing the inward movement of each of said mounting members; and means actuated by outward movement of one of said mounting members for applying an inward force to, the other of said mounting members. n

6. In a self-energizing brake for a rotating cylindrical drum having a pair of arcuate shoes therein and a hydraulic actuating arrangement for moving one end of each shoe into engagement with the drum with a desired actuating force, an equalizing arrangement including: separate mounting members for the other ends of each of said shoes, each member providing for at least limited pivotal movement of that end of each shoe and for at least-limited movement of each shoe in a direction generally parallel to a chord through the ends thereof; fixed stops limiting the inward movement of each of said mounting members; and a lever pivotally mounted intermediate its ends and actuated at one end by outward movement of one of said mounting mem' bers for causing the other end to apply an inward force to the other of said mounting members.

7. In a selfenergizing brake for a rotating cylindrical drum having a pair of arcuate shoes therein and a hydraulic actuating arrangement for moving one end of each shoe into engagement with the drum with a desired actuating force. an equalizing arrangement including: separat: mounting members for the other ends of each of said shoes, each\ member providing for at least limited pivotal movement of that end of each shoe and for at least limited movement of each shoe in a direction generally parallel to a chord through the ends thereof; fixed stops limiting the inward movement of each oi said mounting members; a lever pivotally mounted in- Iterrnedlate its ends and actuated at one end by NILS O. MYKLESTAD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number t Name Date 1,736,046 Madden Nov. 19, 1929 1,804,697 Lord May 12, 1931 1,806,151 Dick May 19, 1931` 2,115,230

Oliver Apr. 26, 1938 

